Ziegler-Natta and metallocene catalyst systems are well established in the prior art for their use in the polymerization of olefins. The use of Ziegler-Natta catalysts, for example, those produced by activating a titanium halide with an organometallic compound (e.g., trialkyl aluminum), are fundamental to many commercial processes for manufacturing polyolefins. In certain instances the active components of the Ziegler-Natta catalyst have been impregnated into a support, such as an inorganic oxide (e.g., silica) prior to introduction into the reaction zone (see Macromol. Symp., 1995, 89, 563).
Over the past decade, metallocene olefin polymerization catalyst systems have been developed. These systems typically use a Group IV-B metal contain compound having at least one cyclopentadienyl group coordinated to a transition metal atom as, for example cyclopentadiene and bis(cyclopentadienyl) transition metal compounds and an activator, such as an aluminoxane, or a boron or borate compound.
Metallocene catalysts can be employed either as so-called “neutral metallocenes” in which case an alumoxane, such as methylalumoxane, is used as a co-catalyst, or they can be employed as so-called “cationic metallocenes” which incorporate a stable and loosely bound non-coordinating anion as a counter ion to a cationic metal metallocene center. Cationic metallocenes are disclosed in U.S. Pat. Nos. 5,064,802; 5,225,500; 5,243,002; 5,321,106; 5,427,991; and 5,643,847; and EP 426 637 and EP 426 638.
U.S. Pat. No. 5,241,025 teaches a catalyst system having an activator component formed from a Group III-A element activator. This activator reacts with a ligand of the Group IV-B metallocene complex and an anion which is bulky and non-coordinatable with the Group IV-B transition metal cation produced. Similarly, U.S. Pat. No. 5,198,401 teaches the formation of an ionic catalyst composition using a bis(cyclopentadienyl) Group IV-B metal complex and a boron containing activator. Both of the above teachings are directed to homogeneous metallocene polyolefin catalyst systems.
Another widely used activator for metallocene catalyst systems are aluminoxanes. These compounds are olgimers or polymeric aluminum oxy compounds containing chains of alternating aluminum and oxygen atoms with alkyl groups pendent from the aluminum atoms. The aluminoxanes are normally formed by the reaction of water and an aluminum alkyl which may also contain a halo or alkoxy group, as disclosed in EP-A-338,044. The most preferred aluminoxane is methylaluminoxane (MAO). It is known that transition metal catalysts require large quantities (e.g., Al to transition metal molar ratio of about 500 or greater) of activator (e.g., aluminoxane) to achieve commercially suitable activity. Conventionally, these activators are normally separately formed and then combined with the catalyst precursor compound. Such activators are expensive and difficult to handle due to their pyrophoric properties and unstable character. Further, catalyst systems formed with these activators are difficult to effectively anchor or immobilized onto a support and, therefore, the catalyst tend to resolubilize from or leach out of the support causing fouling within the polymerization reactor.
Several patents disclose the formation of aluminoxanes from an aluminum alkyl compound and hydrated silica. U.S. Pat. No. 4,904,631 teaches the formation of an aluminoxane activator from a trialkyl aluminum with silica having 6 to 20 wt percent water. The initially formed activator is subsequently used with an early transition metal compound to provide a catalyst composition of low activity. Similarly, U.S. Pat. No. 5,008,228 forms its aluminoxane cocatalyst from an aluminum alkyl and a silica having 10 to 50 weight percent water. The formed aluminoxane is added to a metallocene compound to provide a heterogeneous catalyst for the polymerization of olefins. In U.S. Pat. No. 5,629,253, one is taught that hydrated silica should be reacted with an aluminum alkyl in an amount to have a molar ratio of metal to water of greater than 0.7 and the water content of the silica should be from about 7 to 15 weight percent to provide a desired aluminoxane which can then be combined with a metallocene compound.
The required use of aluminoxane in large quantities to provide a catalyst of suitable activity, the need to initially form the aluminoxane followed by its combining with certain catalysts compounds in a multi-step process, the sensitivity of metallocenes to commonly encountered impurities and the poor morphology of resultant polymer product are all known disadvantages of such catalyst systems.
Recently, much interest has centered on the use of late transition metal (e.g., Fe, Co, Ni or Pd) bidentate and tridentate based catalyst compositions because of their low electrophilicity and consequent improved tolerance to polar functionalities. Representative disclosers of such late transition metal catalysts are found in U.S. Pat. No. 5,880,241 and its divisional counterparts U.S. Pat. Nos. 5,880,323; 5,866,663; 5,886,224; and 5,891,963, and PCT International Application Nos. PCT/US98/00316; PCT/US97/23556; PCT/GB99/00714; PCT/GB99/00715; and PCT/GB99/00716. These metal compounds typically exhibit good activity when they are used with large amounts of aluminoxane activators to generate the cationic catalyst specie. However, the presence of large amounts of aluminoxane in such systems cause chain transfer reaction to occur and thereby predominantly produce low molecular weight oligomer products.
There are a number of factors used to evaluate a catalyst system, such as its activity, that is to say the amount of catalyst required for economic conversion of a given amount of olefin, the product conversion time and the product yield. Further, the stability and ease of handling of catalyst components and the resultant system are other factors which effect the choice of commercial embodiments. For example, coordination catalysts are known to be extremely sensitive to moisture and air and their activity is greatly reduced or destroyed by such elements. Still further, the ability of a catalyst system, especially a coordination catalyst, to be utilized as a heterogeneous catalyst is of commercial consideration. Such systems are utilized in slurry polymerization processes where the monomer, catalyst and diluent are continuously fed into the reactor and the solid polymer product so produced is periodically withdrawn.
Thus, there has been a continuing search to develop a coordination catalyst system, preferably a heterogeneous coordination catalyst system, which demonstrates high catalyst activity, is free of reactor fouling, produces polymer products having good resin morphology while simultaneously being very process friendly (e.g., easy to make) and inexpensive to make.
There has also been a particular need to discover compounds which are less sensitive to deactivation and/or less hazardous and still suitable as activating components in coordination catalyst systems.
It would be desirable to provide heterogeneous polymerization catalyst compositions with high catalytic activity for the production of olefinic polymers and copolymers. It would be also desirable to provide such a catalyst composition of high catalytic activity which does not require the use of aluminoxane. It would be further desirable to produce said heterogeneous catalyst compositions by a single step process. It would still further be desirable to provide a process for the polymerization of olefins, such as ethylene alone or with higher olefins or functional olefins, using said heterogeneous catalyst composition.